This invention relates to a process for the remanufacture of electrical transformers and, in particular, to a novel and improved process which economically and quickly removes water and other contaminants such as acid, sludge, dirt and the like from the transformer coil/core assembly without material damage to the transformer insulation.
Electrical power and distribution transformers are commonly used in an oil-filled tank or vessel. The filler oil acts as an insulator and coolant to keep the transformer coil/core assembly operating at peak efficiency. Over time the dielectric properties of the oil can deteriorate and substantially reduce the efficiency and operating safety of the transformer. Contaminants such as, water, dirt, acid and air can enter a transformer tank during normal usage and degrade the oil and coil/core assembly. As a result, these transformers must be subjected to a remanufacturing process from time to time to restore their efficiency and operating safety.
According to one known remanufacturing process, water is removed by a hot air drying procedure that involves baking the transformer coil/core assembly in a oven at 275.degree. F. for eight to ten hours. This process has several disadvantages. First, it is highly energy intensive. Second, the number of units that can be treated in a single batch is limited by the size of the oven thereby putting extreme limitations on production capacity as well as ruling out almost completely "same day service." Third, the hot air drying process makes the transformer paper insulation (kraft paper) brittle which severely limits the longevity of the transformer coil/core assembly. Fourth, an undesirable bi-product of the baking process is oil smoke (due to the transformer oil) which causes environmental concerns. Fifth, contaminants such as dirt and sludge are baked into the coil/core assembly and remain there after the assembly is reinserted into the transformer tank and reoiled. Sixth, should there be a delay between removal from the oven and the reoiling process, atmospheric water and air can be reabsorbed by the assembly. Despite all these disadvantages, the hot air drying procedure is an industry-wide accepted method and has been so for many years.
Another known process described in U.S. Pat. No. 4,425,949 acts to remove from a transformer contaminants such as polychlorinated biphenyls and diphenyls (PCB's), water and air. This process employs so-called "substitute oils" that react with the PCB's to form an azeotrope. According to the process, a closed system is established in which the transformer tank is connected to equipment which first evacuates the tank and then flushes the tank and the transformer coil/core assembly with a substitute oil vapor. The exiting vapor is then processed to separate the contaminants from the substitute oil which is then reused. Optionally, the transformer can be subjected after the vapor flush to a hot liquid flush for the purpose of rinsing. However, the disclosed equipment is rather elaborate and expensive and is capable of processing only one transformer at a time. More importantly, the substitute oils disclosed in the patent (methylene chloride, carbon tetrachloride, chloroform, trichloroethylene, perchloroethylene, bromochloromethylene and FREON 111 and FREON 113 (1, 1, 2-trichloro-1, 2, 2-trifluoroethane) are rather hazardous substances which are harmful to the personnel who must handle the substances as well as to the environment.